The present invention relates to a process for producing argon by separation from oxygen and nitrogen in an air fractionating process.
It is known that separation of argon from other atmospheric gases has so far been carried out by drawing gas from an air fractionating column at a height which is intermediate between the bottom and the top on a column zone which is known to correspond to the maximum enrichment of argon on the basis of theoretical considerations or practical measurements. In air fractionating plants with double rectification for producing oxygen and nitrogen, the drawing of gas for recovering argon is carried out from the upper or rectification column.
It is also known that the separation of gaseous argon is difficult, though it is the most usual rare gas of the atmosphere, due to the fact that its boiling temperature is near to the ones of oxygen and nitrogen and intermediate between both. Vapour drawn from the rectification column was hiterto forwarded to the top of an auxiliary operation column, called "argon column", in which the vapor was partially freed from its O.sub.2 component and from which a product containing from 60 to 99% in volume of argon, from 0,3 to 20% of oxygen and again from 0,3 to 20% of nitrogen was released.
Consequently at the outlet of the argon column the product has to be again purified from oxygen and nitrogen and this is usually accomplished for O.sub.2 by combining it with hydrogen on particular purifying agents, so that O.sub.2 and H.sub.2 combine mutually thus producing water.
Such process involves nevertheless some inconveniences such as the complexity of the operations to which the product must be subjected before obtaining argon substantially free from O.sub.2.
It has to be chiefly taken into account the high cost of purifying agents, generally catalysts (for instance palladium based), and of reacting hydrogen and moreover the fact that the obtained product must be dried and freed from hydrogen and nitrogen in excess.